Such a device for taking inspiratory and/or expiratory, i.e., defined breathing gas samples, which belong to a defined phase of breathing, from the breathing gas of a patient for analyzing substances contained in the breathing gas samples is disclosed in DE 196 19 763 A1, where certain breathing gas samples from the phase of inspiration and/or expiration are enriched by a reversing valve, but no provisions are made for the continuous measurement of defined breathing gas samples only from breaths following each other in time.
The analysis of or determination of concentrations in breathing gas samples in such a way that the analysis or determination is resolved for individual breaths makes it possible to determine and monitor the status of a patient, for example, based on the expired concentrations or quantities of a characteristic active ingredient such as propofol and/or metabolites thereof or of substances formed endogenously, for example, acetone, which can be found in the expired air.
When analyzing breathing gas samples of patients who are respirated mechanically (also known as ventilated) or are not able to cooperate by means of sensors or other measuring devices, the response times of the measuring means used must be coordinated with the respiration rate in order to make possible informative measurements during the phase of inspiration and/or the phase of expiration. The response times of many measuring systems do not meet these requirements concerning the determination of the concentrations in such a way that the determination is resolved for individual breaths, so that these measuring systems can be used for breathing gas analysis to a limited extent only.
Exact assignment of the measurement results obtained to defined phases of breathing, for example, inspiration, expiration, end tidal phase, etc., is very important for the interpretation of measurement results obtained for breathing gas samples, because they provide information on the origin of the measured substances or metabolites, for example, from the room air, from the upper airways or from the alveoli.